straight answer of the thread title: anything that is an object (i.e. anything that is not:
null, a string/boolean/number literal) is passed by reference. that includes: HTML elements, Arrays, JSON objects, object literals, Dates, Functions and many more.
The computer is always right. The computer is always right. The computer is always right. Take it from someone who has programmed for over ten years: not once has the computational mechanism of the machine malfunctioned.
André Behrens, NY Times Software Developer